The article ‘Content-based image retrieval by viewpoint-invariant color indexing’ by Theo Gevers and Arnold W. M. Smeulders, Image and Vision Computing 17 (1999), pp. 475-488, discloses a method for image retrieval using color information indexing. Large amounts of (picture) files can be analyzed by using the color information in the pictures. The method may be applied to find a large number of files in which the same object is contained as in an image example (but possibly from a different viewing angle, and lighting conditions). Only the color information in the files is used in this method.
American patent application US2003/0208482 discloses systems and methods of retrieving relevant information from Internet pages, using keywords or combinations of keywords. The disclosed searching and ranking method is completely text-based.
International patent application WO02/008948 describes a method and system for indexing, searching, identifying and editing portions of electronic multimedia files. For example, textual information in a graphic form in multimedia files may be extracted therefrom and added to the file as a tag or bookmark.